The invention pertains to a filter head, designed to hold at least two filter elements.
In an internal combustion engine, the fuel is cleaned by two filter elements. These are installed in a stationary filter head. A shutoff lever is used to determine manually the number of filter elements through which the fuel will flow. During normal operation, for example, the fuel will flow through both elements, whereas, during maintenance work, it will flow through only one filter element, which allows the other filter element to be replaced.
A filter head with integrated feed channels and return channels, with two filter elements, and with a shutoff lever is known from U.S. Pat. No. 1,861,805. The lever is connected nonrotatably to a switching drum, so that turning the shutoff lever has the effect of actuating the switching drum, which in turn controls the flow of liquid through the feed and return channels. The switching drum and the filter head are sealed off radially from each other. So that the switching drum is free to rotate inside the filter head, an appropriate annular gap must be present.
A critical aspect of a filter head of this type is that, when one of the filter elements is to be replaced and the filter element has therefore been removed from the filter head, fuel escapes from the filter head through the annular gap. The classification societies for marine engines specify that no leakage may occur while the first filter element is active and the second filter element is being replaced. For this reason, this filter head cannot be used without supplemental measures such as the installation of nonreturn valves. Another critical point is that the shutoff lever must be turned against the force caused by the pressure of the fuel. In the case of a common-rail system, the low-pressure pump produces a pressure level of approximately 8 bars, which means that the shutoff lever is difficult to actuate.